feat(context): add MCP result compactor for tool output shadow path

Introduce off/shadow/active compaction for large tkmind read/research and
excel report payloads with optional Redis-backed ctx_fetch handles, keeping
fail-open behavior when storage is unavailable.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/check-mcp-compactor-local.mjs

@@ -0,0 +1,44 @@
+#!/usr/bin/env node
+/**
+ * Local smoke for MCP result compactor (Phase 1-B).
+ */
+import {
+  applyMcpCompaction,
+  createMemoryCompactStore,
+  fetchCompactPayload,
+  resetMcpCompactStoresForTests,
+  resolveMcpCompactMode,
+} from '../mcp-result-compactor.mjs';
+
+resetMcpCompactStoresForTests();
+const store = createMemoryCompactStore();
+const payload = `section-${'x'.repeat(6000)}\nfooter-line`;
+
+const shadow = await applyMcpCompaction(payload, {
+  kind: 'tkmind_read',
+  env: { MEMIND_MCP_COMPACT_MODE: 'shadow', MEMIND_MCP_COMPACT_BUDGET_CHARS: '800' },
+  store,
+});
+if (shadow.text !== payload || shadow.mode !== 'shadow') {
+  throw new Error(`shadow mode should keep original payload: ${JSON.stringify(shadow)}`);
+}
+
+const active = await applyMcpCompaction(payload, {
+  kind: 'tkmind_read',
+  env: { MEMIND_MCP_COMPACT_MODE: 'active', MEMIND_MCP_COMPACT_BUDGET_CHARS: '800' },
+  store,
+});
+if (!active.compacted || !active.handle) {
+  throw new Error(`active mode should compact payload: ${JSON.stringify(active)}`);
+}
+const restored = await fetchCompactPayload(active.handle, { store });
+if (!restored.ok || restored.text !== payload) {
+  throw new Error(`ctx_fetch restore failed: ${JSON.stringify(restored)}`);
+}
+
+console.log('MCP_COMPACTOR_LOCAL_OK:', {
+  mode: resolveMcpCompactMode(),
+  shadowSavedRatio: shadow.stats?.savedRatio ?? 0,
+  activeSavedRatio: active.stats?.savedRatio ?? 0,
+  handle: active.handle,
+});